1. Technical Field
The present invention relates to a piezoelectric resonator for an oscillator and a surface mount type piezoelectric oscillator with which an inconvenience of adjustment work by using a small adjustment terminal provided on a side of a package is eliminated.
2. Related Art
In a mobile communication market, many manufactures of mobile terminal devices promote modularization of parts and components by their functions in consideration of assembly designs, maintenance and handleability of the electric components and compatibility of the components among devices. At the same time, there are strong requests for downsizing of the devices and low manufacturing costs with the advance of the modularization.
There is a trend of the modularization especially in circuit parts whose functions and hardware configurations are established and for which high stability and enhanced performance are further requested. As such circuit parts, a reference oscillation circuit, a phase-locked loop (PLL) circuit, a synthesizer circuit and the like can be named. When these parts are modularized as a package, there is an advantage that a shielding structure can be more easily secured.
As the electric parts which are modularized and packaged with associated parts for surface mounting, for example, there are a piezoelectric resonator, a piezoelectric oscillator, a surface acoustic wave (SAW) device and the like. For example, a module having a two-story structure as shown in FIG. 6 can be adopted in order to maintain performances of the electric parts and to further minimize the size of the module.
JP-A-2001-177346 and JP-A-11-355047 are a first example of related art. FIG. 6A is a longitudinal sectional view showing a structure of the two-story type module of a surface mount type piezoelectric device (a crystal oscillator) as the first example. A crystal resonator 100 and an under part member 107 (an IC parts unit) are shown in FIG. 6A. The crystal resonator 100 has a crystal resonant element 103 in a container consisting of a ceramic case body 101 and a metal lid 102. The under part member 107 has an IC part 106 that includes an oscillation circuit, a temperature compensating circuit and the like. The IC part 106 is assembled in a form of a bare-chip, placed in an empty space 105a in a case 105 that is attached to the bottom face of the crystal resonator 100, and sealed. As described in the first example, when such crystal oscillator is mounted on a printed wiring board, an external electrode 105b provided on the bottom face of the case 105 is soldered.
JP-A-2000-278047 is a second example of related art. FIG. 6B is a sectional view showing a structure of a two-story type module of the crystal oscillator as the second example. As shown in FIG. 6B, the empty space 105a in the under part member 107 is opened downward and the opening of the empty space 105a is closed with a bottom plate 105c if required. These are the different features from those of the above-described first example with reference to FIG. 6A.
In the above described first and second examples, an adjustment terminal 110 for adjusting a regulator circuit included in the IC part is provided on the outer surface of the case body 101. The adjustment terminal 110 is used, for example, for rewriting a value of an element (temperature compensation parameter) consisting the temperature compensating circuit in the IC part. This rewriting is conducted by making an unshown probe contact with the adjustment terminal 110 and then putting data through the probe. When a manufacturer of the oscillator supplies the crystal resonator 100 that is assembled with the case 105 containing the IC part 106 to an assembly company (for example, a cellular phone manufacturer), the oscillator manufacturer adjusts the element value by using the adjustment terminal then ships the oscillator to the assembly company. Therefore, the assembly company can use the piezoelectric oscillator without any adjustment work.
However, the size of the adjustment terminal 110 has to be small since it is provided on the side face of the small oscillator whose size is about some ten millimeter in length and width. Accordingly, the adjustment work with a probe becomes extremely delicate and an inefficient work. Moreover, the size of the adjustment terminal 110 cannot be made further smaller because a sufficient area with which the probe contacts has to be secured. This also puts a limit on the size of the oscillator, and this becomes a problem when there is a request for a smaller size oscillator. Solution to such problem is now strongly needed.
Meanwhile, assembly companies lately purchase less completed oscillators in which the crystal oscillator is assembled with the IC part in order to reduce costs. Instead, the assembly companies buy only the crystal resonator part of the oscillator and assemble it with the IC part by themselves. In this case, if the adjustment work is conducted by making the probe contact with the adjustment terminal provided on the side of a device such as a cellular phone after the completed oscillator is embedded in the device, it could be difficult to perform the adjustment work in such a way that other parts around the terminal provided on the side of the product hamper the work. In this way, the adjustment work could become difficult depending on layouts. Therefore, an enough space between the oscillator and the adjacent other parts should be secured for the probe to be interposed therebetween in order to perform the adjustment work. This space becomes a problem when the device is needed to be downsized.